Fuel cells are useful for generating electrical energy based on an electrochemical reaction involving hydrogen and oxygen. There are several types of fuel cell including polymer electrolyte membrane (PEM) fuel cells and phosphoric acid fuel cells (PAFC). Providing and maintaining a sufficient amount of phosphoric acid, which serves as a liquid electrolyte, is one of the issues associated with PAFCs. Once the phosphoric acid evaporates, the PAFC fails so extending the time during which the PAFC has sufficient phosphoric acid increases the useful lifetime of the PAFC.
Some known PAFCs include an uncatalyzed condensation zone on the cathode and anode substrates where evaporating phosphoric acid may be captured. While such condensation zones have some use in this regard, they reduce the area of the electrode substrates that is available for the electrochemical reaction and, consequently, reduce the electrical output capacity of the PAFC.
Some proposed fuel cell configurations include a bipolar plate with a porous layer that may store some phosphoric acid. Such arrangements typically include a solid separator plate against the porous layer to prevent acid migration in between cells. While such separator plates are useful for that purpose they introduce other issues. For example, thermal and electrical transport between cells of a fuel cell stack assembly should be maximized but a solid separator plate tends to reduce thermal and electrical conductivities. Another limiting factor has been that previous techniques for manufacturing such separator plates are expensive. Adding such a plate to each cell increases cost for a cell stack assembly or power plant that includes many cells.
There is a need for improvements in the way in which phosphoric acid is maintained in a PAFC.